We continued to evaluate possible contribution of ethanol on dopamine (DA) metabolism using the LC/ESI-MS/MS method that has been developed in our laboratory. DA is metabolized by monoamine oxidase (MAO) to 3,4-dihydroxyphenylacetaldehyde (dopaldehyde, DOPAL) which is a substrate for aldehyde dehydrogenase-2 (ALDH2). Tetrahydropapaveroline (THP) is a condensation product of DOPAL and DA and can be determined simultaneously along with DA and SAL using the LC/ESI-MS/MS method established previously. As the abnormal DA metabolism appears to be the target for discovering biological markers for alcoholism, we continued our efforts to develop a strategy to survey DA-metabolism using a sensitive mass spectrometric analysis method and stable-isotope labeled DA. Once candidate metabolites are identified, we will examine their levels in human alcoholics in comparison to control subjects to identify better markers for alcoholism and potential therapeutic target events in DA metabolism.